I put bleach, drain cleaner, ran water down it a few times( twice 2 and a half gallon pail and once 5min of water from hose). It drains well but smell starts up in a few min. What else can I do?

When you look inside the drain, do you see standing water ?

Back to you... Milo

Yes there is standing water about 10 inches from top. The level of water has not changed and has always been there.